Piezoresponse Force Microscopy

Piezoresponse force microscopy is a Contact AFM technique to measure sample displacement out of the sample plane in response to an applied AC bias. The method is most directly applicable to piezoelectric samples such as lead zirconia titanate, but can also work for electrostrictive samples such as lead magnesium niobate, and has been used on ferroelectric materials such as barium titanium oxide.

With the SPM in Piezoresponse Mode, the tip is engaged with the sample and an AC voltage is applied between tip and sample during scanning. A responsive sample expands and contracts in synchronization with the applied voltage. By feeding the photodetected cantilever deflection signal into a lock-in amplifier whose reference signal is the applied AC bias frequency, background topography is suppressed from the resulting image which features only the sample surface height changes induced by the applied field.

Piezoresponse imaging does not require additional dedicated hardware and works with both fixed tip/rastered sample (MultiMode) and fixed sample/rastered tip (Dimension) SPMs. There are several consequences of the need to form a circuit to bias the sample:

• The sample must be electrically connected to the sample platform (e.g., with silver paint):

• Though a light imaging force best preserves samples, the tip must stay in contact with the sample to maintain the applied tip/sample voltage. A particularly rough sample may require a higher load force, higher gains or slower scan speeds to ensure a continuous electrical connection.

• A conductive cantilever:
  • MESP
  • NPG
  • SCM-PIC
  • SCM-PIT
• Because active tip cantilevers are not conductive, PR is not operable with Actuated Probe or dual scan.
• Piezoresponse imaging may be performed in a nonconducting fluid. In a conductive fluid, a conductive cantilever must be insulated from the fluid, except at the tip; this is difficult to accomplish.

Steps to acquiring PRM data:

1. Piezoresponse Procedure Set Up
2. Write an Area in the Piezoelectric Sample
3. Image the Written Area
4. Optimize the Image
5. Simultaneous Multiple Optimizations

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